1. Field
The present invention relates to an apparatus and method for controlling a disk drive servo, and more particularly, to an apparatus and method for controlling a servo when moving between layers of a multi-layered disk.
2. Description of the Related Art
Generally, optical disks, which are used as storage media of optical disk drives, can be classified as reproduction-only optical disks such as Compact Disc-read only memory (CD-ROM), writable-once optical disks such as Compact Disc-recordable (CD-R), and rewritable optical discs such as Compact Disc-rewritable (CD-RW), according to use purposes. These various types of disks have specific usage purposes and are widely used. With the development of large-storage capacity disks such as Digital Versatile Discs (DVDs), optical disks are being developed into media functioning as peripheral devices of PCs, for recording not only PC data but also a variety of video and/or audio data.
In particular, research into optical disk drives using multi-layered disks has been conducted in order to increase a data storage capacity of the optical disk. In particular, research into high-density multi-layered optical disk drives that use blue rays and relatively large numerical apertures (NA) has been actively conducted.
A spherical aberration caused by an error to the thickness of layer of an optical disk is proportional to NA to the power of 4. In particular, in the case of high-density disks using blue rays (Blue-Ray Discs), an error in the thickness of a protective layer, even if the absolute value of the thickness error is very small, causes a spherical aberration, which is not negligible. Thus, most high-density optical disk drives use spherical aberration correction units.
Spherical aberration correcting techniques are disclosed in Korean Patent Publication No. 2006-106882 and Japanese Patent Publication No. 2003-22545.
According to the conventional art, when there is a need for a layer jump in a multi-layered optical disk drive, generation timings of signals (e.g., a kick signal and a brake signal) required to move an objective lens of a pickup of an optical disk in order to focus light on a target layer are determined by referring to a focus error signal. When a spherical aberration is not accurately corrected, the magnitude of the focus error signal is changed, and the waveform thereof is distorted. Accordingly, while a spherical aberration correction unit is being driven or the objective lens is moving in order to achieve a layer jump, the focus error signal is distorted, and thus errors are highly likely to occur in the generation timings of the kick signal and the brake signal. Moreover, during driving of a spherical aberration corrector, servo control is unstable even with relatively small external disturbance due to a difference between a spherical aberration amount and a layer on which a beam is currently focused.